When you talk about free-form hull design the J Boat series should come to mind. In fact, you could say that the current trend toward clean, unaffected hull shapes was started by the little J/24 when it broke away from the contorted Quarter Tonners of 10 years ago. Perhaps the best evidence of this success in pure boat speed shapes is the J/35 that continues to drive owners of bigger boats crazy. J Boats sticks with smoothing out the lines, avoiding fads and fashions and concentrates on effective sailing length and well balanced performance. The new J/39 is J Boats' attempt at combining comfort and speed.

A photo of a J/39 sailboat.

A J/39 sails hard into the wind. Photo courtesy of Wikimedia Commons



The Js have always been moderate in their general dimensions. The new 39 has a D/L of 168 with 12,900 pounds of displacement on a 32.5 foot waterline length. Beam is 12 feet 5 inches. To put that in perspective, consider that the 39 is an inch wider than my Valiant 40, which I used to think was fat. All rules place a lot of weight on beam in assessing boat speed: Fat is slow and skinny is fast. This has taught yacht designers to use the beam-to-rule advantage and, at the same time, gain the comfort elements that naturally come with increased beam. So skinny may be fast, but fat is not always slow.

Note the short ends of the 39 and the 54 degree stem angle. This angle is identical to the stem/bow angle on Heart of Gold. The rudder has been pushed aft just as far as possible. The blade is long on root chord and has straight leading and trailing edges. The keel has no bulb, no tuna tail, no curving edges and no fillets. It's just a big straight fin. The boat is very fast and is doing well on the race course against some very exotic IMS competition. Note the sweet line of the immersed canoe body and the lovely sweep of the sheer.

Looking at the deck plan of the 39, we can easily see that the boat is wide and maximum beam is at station 6. The line of the deck forward is on the full side indicating some flare to the topsides forwards. Once designers broke away from the girth measurement constrictions of the IOR, bow sections began to show some added volume and power with no sacrifice of upwind speed at all. Of course, the clean run with straight buttocks aft is another result of losing the girth controls. Note that the transom in plan view shows a tangent at centerline. This shape is in contrast to the deadrise shape of Heart of Gold. (Deadrise is the angle that the hull section makes with horizontal. A deep V-hull would be said to have high deadrise and a flat bottomed boat would have no deadrise.) If you have a wide stern with no deadrise, you run the risk of picking up a lot of wetted surface aft and creating a sticky boat in light air. The moderate beam aft of the J/39 can use the flat run effectively.

Interiorwise, the J/39 exceeds the IMS 100 point interior regulations. These regulations were introduced to reward boats with complete interiors that enhanced their dual purpose nature as racer-cruisers. Certainly, this does introduce another rule-driven element that can be abused and optimized to the letter of the rule, but this potential abuse is not evident in the layout and photos of the J/39's interior. The layout is old basic plan A and will work well for the cruising family. The interior finish is attractively done in white Formica with teak trim.

Looking at the sail plan, we see a tall rig with a SA/D of 23.3 and swept back triple spreaders. Why sweep the spreaders aft? Looking at the interior layout, you can see that the main bulkhead is a natural for mounting the chainplates and the mast fits nicely into the head compartment. As far as performance goes, the swept spreaders combines some fore and aft stiffening with athwartships stiffening. This means that for a bendy rig you need to carry your lower shrouds loose to permit mast bend. If you snug up on the lowers, you are going to reduce mast bend potential. Some racers would prefer to keep these two functions separate so that fore and aft shape is independent of athwartships shape, but this would require a babystay and more active mast bend control.

The deck has been designed for racing efficiency, and I think you would be surprised at just how well this works for cruising. Generally, cruising boats have atrocious deck layouts with every sail adjustment requiring maximum effort to gain minimum effect.

The J/39 has no seatbacks and no cockpit coamings. This is a problem when you are anchored and are trying to find a comfortable place to sit and read in the cockpit, but no problem underway at 20 degrees of heel. The wide uncluttered side decks make for close sheeting angles and easy movement fore and aft.

The hull shape of the J/39 makes it potentially effective in a wide variety of racing rule formats. You could certainly open some eyes in your local PHRF fleet by showing up at the starting line with this beauty.

Boat Specifications
LOA39.5'
LWL32.5'
Beam12.5'
Draft7.2'
Displacement12,900 lbs.
Ballast5,900 lbs.
Sail Area804 sq. ft.
SA/D23.3
D/L167
AuxiliaryYanmar 36MF 28 hp
Fuel25 gals.
Water38 gals.

 

SAILINGlogo-115This story originally appeared in Sailing Magazine, and is republished here by permission. Subscribe to Sailing.

 

 

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